1. Field of the Invention
The present invention relates to a cooking utensil, and particularly, to a cooking utensil which preserves heat entrapped during cooking by having a double-layered wall structure and a method of fabricating such cooking utensil.
2. Discussion of the Related Art
Various types of cooking utensil are known and used in a kitchen. Such cooking utensil is made of one or more layers of stainless steel and has a single layer bottom. The single layer bottom is good for directly transmitting heat to the food contained in the utensil, but also causes burning of the food when carefully not attended to.
To solve the above problems, a cooking utensil having a double-layered structure has been proposed for preventing burnt food and to improve food flavor. One of such ideas is published in Korean Utility Laid-Open Publication No. 85-7307 which teaches that paraffin is injected between a space provided by a double-layered structure and an air-hole is established thereon. Instead of charging the space with paraffin, a structure into which a fluid of heat-medium is injected and sealed is disclosed in Korean Laid-Open Publication No. 97-4035. Moreover, a pot of a double-layered structure and a pot having a double-layered structure into which a working fluid is injected are taught by Japanese Laid-Open Publication No. 56-169825.
In such pots having the above-mentioned structures of the related arts, the gaps between the double-layered structure are filled with heat media to provide even-heat distribution and to save heat energy. Unfortunately, the structures of the related arts are first formed prior to injecting or filling the space formed betweeen walls with heat conductive substances. Thereafter, the outer wall is sealed or a valve is securely placed to prevent the heat conductive substances from leaking out. Such process increases manufacturing cost and decreases production yield.
The roaster of a double-layered structure, into which a heat conductive substance is injected according to the related art, generates high pressure due to internal expansion. To release the pressure safely, the roaster of the related art uses the method of installing a pressure control valve, establishing an inner shell of which shape is easily modified in accordance with the pressure, or reducing the pressure by forming a weak portion on an inner shell.
When the pressure control valve is embodied, the structure and the manufacturing process of the roaster become complicated as well as it is inconvenient to use the roaster due to the pressure control valve. Moreover, forming a weak inner shell reduces the life-span of the roaster. Also, the method of manufacturing a cooking utensil of a double-layered structure by depositing a space between the layers with a heat conduction medium and by sealing a deposit hole is troublesome and generates a leakage of the heat conduction medium due to the weak joint around the deposit hole. As a result, there is still no satisfactory method of sealing the heat conduction medium between the shells.